The inventive concepts described herein relate to an optical communication system, and more particularly, relate to an optical line terminal and an optical network unit capable of supporting an efficient sleep mode for power saving of the optical network unit.
In a next-generation optical communication system, there may be proposed two low-power modes according to a need for power saving. One may be a doze mode and the other may be a cyclic sleep mode. In the two low-power modes, an operation of an optical transceiver may be controlled for actual power saving. Below, the two low-power modes will be described. The doze mode may be a mode where an optical transmitter of an optical network unit is controlled to perform an on operation or an off operation periodically. The cyclic sleep mode may be a mode where an optical transmitter and an optical receiver in the optical network unit are controlled to perform an on operation or an off operation periodically.
As an example, a passive optical network (hereinafter, referred to ‘PON’) may be a next-generation optical communication system. The PON may mean an optical communication network for a subscriber period (i.e., an optical network) which is formed of optical passive elements not requiring a separate power supply. In the PON, an optical splitter may be placed at a specific point of an optical line network from an optical line terminal (hereinafter, referred to ‘OLT’) until a subscriber. A PON manner may have such a structure that a passive element not requiring a power supply is installed at an optical splitter to receive a plurality of optical network units (hereinafter, referred to ‘ONUs’) via one optical fiber.
In the PON, the doze mode and the cyclic sleep mode may operate as follows. The OLT may send a PLOAM (Physical Layer Operations Administrations and Maintenance) control message, indicating possibility of a transition to the sleep mode, to a specific ONU when the specific ONU transitions to a sleep mode. In response to the PLOAM control message provided from the OLT, the ONU may periodically determine whether own state is capable to being switched into the sleep mode. If a transition to the sleep mode is possible, the PLOAM control message indicating possibility of a transition to the sleep mode may be sent to the OLT.
If the ONU transmits and receives a signal indicating a transition to the sleep mode, it may transition to the sleep mode. In the sleep mode, the ONU may operate at a mode, set to an OMCI (ONT Management Control Interface) control channel, from among the doze mode and the cyclic sleep mode.
The doze mode may be a mode where an optical transmitter of an optical module is periodically turned on/off. Thus, since an optical receiver is always turned on, it may receive downward data anytime. However, transmission may be performed only when the optical transmitter is turned on.
The cyclic sleep mode may be a mode where a transmitter and a receiver of the optical module are periodically turned on/off at the same time. Although data transmission and reception are not free by transmitting and receiving data only when both the transmitter and the receiver are turned on, a power consumed at the cyclic sleep mode may be less than that at the doze mode.
If the OLT or ONU does not correspond to a sleep mode operating condition during the sleep mode of the ONT operates, a transition to a normal mode may be performed.
For example, the ONU may detect that traffic is applied to an UNI (User Network Interface) port. This case may include the case that a subscriber turns a computer (e.g., PC) on or the case that a receiver of a VoIP (Voice of Internet Protocol) telephone is on. At this time, the ONU may transmit the PLOAM control message indicating a transition to the normal mode to the OLT.
Alternatively, the OLT may detect that there gets a phone call from the exterior. This case may include the OLT detects a transition to the normal mode prior to the ONU. At this time, the ONU may transmit the PLOAM control message, indicating a transition of a normal mode, or an FWI (Forced Wake-up Indication) bit to the ONU.
A conventional optical communication system may save a power using the normal mode and the sleep mode. However, an operation for saving a power during the sleep mode may not be proposed.